Optical pickups have been used in optical disk drives for reading or writing information from or to an optical recording medium (“optical disk”) such as CD-ROM, CD-R, CD-RW, DVD-RAM, DVD-R, and DVD-RW. The optical pickup is a device for converging a laser beam emitted by a semiconductor laser, which is a light source, on a signal recording surface of an optical disk by means of an objective lens and then detecting a light bounced back from the signal recording surface by means of a light detector equipped with a photo detector (“PD”), which is a light detecting means.
FIG. 9(a) is a plan view indicating the outline of the arrangement of each optical system used on a conventional optical pickup. FIG. 9(b) is a view indicating a polarization surface of an incident light to the optical disk. FIG. 10 is a side view indicating the arrangement of each optical system used on the optical pickup shown in FIG. 9(a).
As shown in FIG. 9 and FIG. 10, the optical pickup comprises a semiconductor laser (“LD”) 11 for dual wavelengths, a diffraction grating (“GRT”) 12 to which the laser beam from LD 11 enters, a beam splitter (“BS”) 13 for reflecting the laser beam from GRT 12, a photo detector (“PD”) 17 that functions as an optical detector placed in the direction opposite to the direction of a laser beam reflecting from BS 13, a raising mirror (“MIR”) 14 that reflects the reflected laser beam for BS 13 again to change its direction, a collimating lens (“CL’) 15 for converging the reflected laser beam from MIR 14, and an objective lens (OL) 16 for focusing the laser beam converged by CL 15 on the signal recording surface of an optical disk 18 and irradiating it. Since MIR 14, CL 15, and OL 16 guide the laser beam on the signal recording surface of optical disk 18, and the returning beam of the laser beam from the signal recording surface to BS 13, they will be referred to as the laser beam guiding components.
The two different wavelengths of the semiconductor laser 11 are used for reading signals recorded on a DVD disk and a CD disk respectively.
In reading signals recorded on an optical disk, laser beams first enter into optical disk 18. The return laser beams from the signal reflecting surface travel again through OL 16 and CL 15, enter into and are reflected by MIR 14 into a different direction, and enter into BS 13. The return beams from the optical disk pass through BS 13, and enter into photo detector (“PD”) 17 of the optical detector. PD 17 detects the change of intensities of the laser beams returning from the signal recording surface.
On a conventional optical pickup 50, as shown in FIG. 9(a), it is designed in such a way that the polarization plane of the laser beam (“polarization plane”) emitted from the LD lies in a substantially horizontal direction, and the polarization plane of a spot of a laser beam that enters into the signal recording surface of optical disk 18 coincides with a radial direction 21 of optical disk 18 as shown in FIG. 9(b).
However, optical pickup 50, shown in FIGS. 9(a) and (b), as well as conventional optical pickups have problems in playing the signal recorded on optical disk 18 in that the playability deteriorates in comparison with an optical pickup having a polarization plane adjusted to a direction 52, which is tilted approximately 45 degrees.